Penn 521190CS ATP World Tour Reg Duty Tennis Ball Case The Penn ATP tennis ball is the #1 choice of ATP players and the offical ball of the ATP. Penn ATP features tournament-grade felt and technical grade rubber core for precise bounces... Penn Tennis Balls | Atp | Regular Duty Size - (See Description) | Color - (See Description) Authorized Penn Dealer. All racquets are strung and ready for the courts! SEE SELLER DETAILS FOR RETURN POLICY.